The present invention relates to valves and more particularly to so-called butterfly valves for controlling fluid flow through a conduit.
Butterfly valves have long been used to control fluid flowing in conduits and problems relating to the general design and constructional features of such valves have been recognized. Generally butterfly valves are formed by a plate-like valving member disposed in a fluid flow passage and supported by a shaft or hinge structure for rotation about an axis transverse to the passage to alter the flow rate. The valving member itself is usually configured so that when moved to a closed position the flow passage is completely blocked by the valving member with a fluid tight seal being formed along the juncture of the valving member periphery and the passage. When moved to its opened position the valving member extends generally parallel to the direction of fluid flow and the fluid can flow around it through the passage. The supporting shaft or hinge usually extends through the passage wall to an actuator operable to control the valving member position.
Butterfly valves employed in closed fluid systems tend to develop leaks along the valve supporting shaft. The shaft is normally subjected to bending forces and therefore must generally be provided with some sort of bearing structure in addition to a shaft seal. Various bearing and seal constructions have been proposed by the prior art to minimize the leakage problem. The proposed constructions have, for the most part, required the usage of multi-part bearing and seal components which increase the cost, complexity and degree of difficulty of assembly of the valves.
The construction of the valving members has also presented problems in many butterfly valve applications. Where the valve is used in a liquid system, the periphery of the valving member must effectively seal against the surrounding flow passage yet be readily opened without tending to stick closed. The valving members are generally urged toward the closed positions by fluid pressure differential forces acting on them and as a result of valve actuator overtravel and these forces tend to jam the valving member into its closed position. Various valving member constructions have been proposed to alleviate this problem. Rubber-like flexible, resilient valving members have been frequently employed to assure positive closure of the valves but many of these constructions have tended to stick closed because of the excessive flexibility of the valving member material which tends to promote not only jamming but wear and abrasion of the valving sealing face. Composite valving members formed of rubber or plastic parts supported by structurally strong components have been proposed. Some of these have employed molded-in steel plates while others have clamped rubber-like valving elements to structurally stronger parts.
Butterfly valves have been proposed for use in automotive fluid systems for controlling the flow of engine coolant to heat exchangers which are used to heat air flowing into the passenger compartment of vehicles. Such valves must be extremely reliable in operation while at the same time being of simple enough design to enable low cost, high volume production with a minimum number of complicated assembly steps. Low cost high volume production tends to dictate the use of a one piece cast valve body defining a tubular flow passage for the liquid.
Prior art butterfly valve constructions utilizing a one piece valve body have encountered assembly problems because the butterfly valving member and its driving shaft must be assembled with the valving member already positioned inside the valve body. To do this the valve body has been provided with shaft supporting openings on opposite sides and the valving member has been positioned within the tubular valve body. The shaft was inserted through the valve body so and a joining operation between the valving member and the shaft was performed with the components of the assembly held together by suitable fixturing. In some proposals the shaft was spot welded to the valving member. In others a one-piece plastic valving member was held in place within the valve body and a serrated shaft was driven through the valving member to create the driving interconnection.
These approaches have in general been either difficult to perform quickly and efficiently or have not produced a sufficiently strong and durable valve, or both.
Still another problem with the one piece cast valve bodies was encountered because the valve body wall itself was used to journal the shafts. This required the use of relatively heavy valve body wall sections and the selection of alloys which functioned well as bearings. These factors added to valve body costs.